1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and the like, and a unit detachably mountable to such an image forming apparatus, and more particularly, it relates to an image forming apparatus having a function for judging a life (service life) of a unit detachably mountable to such an image forming apparatus, and such a unit detachably mountable to the image forming apparatus.
An electrophotographic image forming apparatus as an example of such an image forming apparatus may include, for example, an electrophotographic copying machine, an electrophotographic printer (for example, LED printer, laser beam printer or the like) and an electrophotographic facsimile.
Further, a cartridge detachably mountable to a main body of the electrophotographic image forming apparatus is referred to as a unit which includes at least one of an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, developing means for supplying developer to the electrophotographic photosensitive member and cleaning means for cleaning the electrophotographic photosensitive member. Particularly, a process cartridge is referred to as a cartridge which integrally incorporates at least one of charging means, developing means and cleaning means, and an electrophotographic photosensitive member as a unit which can detachably mounted to a main body of the electrophotographic image forming apparatus or which integrally incorporates at least developing means and an electrophotographic photosensitive member as a unit which can detachably mounted to a main body of the electrophotographic image forming apparatus.
2. Related Background Art
In conventional image forming apparatuses of electrophotographic type such as electrophotographic copying machine and laser beam printers, after an electrophotographic photosensitive member as an image bearing member is uniformly charged, a latent image is formed by projecting a beam corresponding to image information on a surface of the photosensitive member, and the latent image is then visualized by developing means for supplying developer to the latent image, and the visualized image is then transferred from the electrophotographic photosensitive member to a recording medium, thereby forming an image on the recording medium.
As such an image forming apparatus of electrophotographic type, both a monochromatic image forming apparatus and a color image forming apparatus have been put to a practical use.
Further, in the past, while a color copying machine of the electrophotographic type has been manufactured actively, in recent years, compactness of the apparatus has been considered important so as to apply the laser beam system to a desk-top color printer. Due to an increase in memory capacity and CPU performance of a host computer and the popularization of digital cameras and scanners, even for personal use, image processing and color DTP have been affected. And, as the resolving power of image data to be processed is increased, high quality image output of the color printer has been requested.
In monochromatic printers, since a laser-beam system having high image quality, reliability and high speed operation has been normally used in business use, the application of such a system to color processing has highly been requested. However, since there arises a problem that the entire apparatus becomes bulky and complicated due to multi-colorization, in order to promote its popularization in the market, increased compactness, low cost, reliability similar to the monochromatic system, and easy maintenance must be realized.
In order to realize easy maintenance, there has been proposed a process cartridge system in which an electrophotographic photosensitive member, and charging means, developing means and cleaning means as process means acting on the electrophotographic photosensitive member, and a developer container and a waste developer container are integrally incorporated as a unit which can detachably be mounted to a main body of the image forming apparatus. According to such a process-cartridge system, since the maintenance of the apparatus can be performed by the user himself without any serviceman, operability can be improved considerably. Thus, the process cartridge system has widely been used with the electrophotographic image forming apparatus. By using the process-cartridge system, the user can easily replenish the developer and exchange the electrophotographic photosensitive member, which otherwise are troublesome.
Such a process cartridge system is also adopted to the color electrophotographic image forming apparatus. For example, there is a color printer to which a process cartridge integrally incorporating therein the electrophotographic photosensitive member, charging means, cleaning means and developing means can detachably be mounted.
Further, for example, when the consumption conditions of plural color developing devices each having developing means and a developer container are different or when the consumption conditions of the electrophotographic photosensitive member and the developing means are different, in order to cope with this, for example, a developing cartridge for each color including the developing means and the developer container or a photosensitive drum cartridge integrally including the cleaning means, the waste developer container and the electrophotographic photosensitive member, which cartridge is independently detachably mountable to the main body of the apparatus, has been proposed to permit independent exchange and maintenance of respective color developing means and the electrophotographic photosensitive member.
In order to further improve the easy maintenance of the image forming apparatus of the process-cartridge type, it is desirable to timely inform the user of the exchanging time of the cartridge. To this end, it is required that the life of the cartridge be detected correctly.
For example, in the process cartridge integrally including the electrophotographic photosensitive member and at least developing means, when the life of the cartridge is detected, since the life of the electrophotographic photosensitive member does not always coincide with the life of the developing device, in the past, the respective service lives have been detected and the shorter life has been regarded as the life of the process cartridge.
Normally, the detection of the life of the electrophotographic photosensitive member is effected by using, as consumed amount information of the electrophotographic photosensitive member, the image formed copy number or the number of revolutions of the cylindrical electrophotographic photosensitive member (photosensitive drum). On the other hand, the detection of the life of the developing device is effected by seeking a developer remaining amount as consumed amount information of the developing device by measuring the developer remaining amount by means of an optical system or a capacitance measuring system or by guessing a developer amount (developing amount) used in development on the basis of the number of pixels of the latent image formed on the electrophotographic photosensitive member, which is called as xe2x80x9cpixel countxe2x80x9d.
However, in actuality, even if the image formed copy number or the developer remaining amount does not signify the end of the life of the cartridge, normal image formation may not be attained.
For example, if image formation with a low image ratio is effected frequently, the developer will deteriorate faster than the normal case. in this case, even if the image formed copy number or the developer remaining amount does not signify the end of the life of the cartridge, since the correct image formation becomes impossible, it must be regarded that the life of the cartridge is expired.
Accordingly, the life of the cartridge (unit) can be not always judged correctly only on the basis of usage amount information, such as the image formed copy number or the developer remaining amount, and, thus, it is requested to provide an apparatus whose life, which cannot be judged only on the basis of the usage amount information, can also be judged.
The present invention aims to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide an image forming apparatus which can correctly judge the life of a unit which can detachably mounted to a main body of the apparatus, and a unit detachably mountable to such an apparatus.
Another object of the present invention is to provide an image forming apparatus comprising a unit detachably mountable on the image forming apparatus, the unit having developing means for developing a latent image formed on an image bearing member, and life judging means for judging the life of the unit on the basis of the developing bias applied to the developing means.
A further object of the present invention is to provide a unit detachably mountable on an image forming apparatus, comprising developing means for developing a latent image formed on an image bearing member, and a memory, wherein the memory stores a value of developing bias applied to the developing means.
A still further object of the present invention is to provide an image forming apparatus comprising a unit detachably mountable on the image forming apparatus, the unit having developing means for developing a latent image formed on an image bearing member, and life judging means for judging a life of the unit on the basis of the image density of a test pattern formed by the developing means.
A further object of the present invention is to provide a unit detachably mountable on an image forming apparatus, comprising developing means for developing a latent image formed on an image bearing member, and a memory, wherein the memory stores image density data when gradation control is effected.